The concept-of using electronic stimulation systems to control pain by nerve or muscle stimulation is well known. Spinal cord stimulation (SCS) is a technique that has been used for pain management since the 1960s. SCS systems feature a pulse generator, discussed further below, coupled to one or more percutaneous leads having a plurality of electrodes (systems may also use a paddle-type lead that requires insertion by laminectomy). The leads are positioned within a patient's epidural space, parallel to the axis of the spinal cord. The leads' electrodes are used to deliver a particularized electric field to a specific region of the spinal cord or surrounding tissue. Applying an electric field across one or more nerve bundles and/or nerve roots can produce paresthesia, or a subjective sensation of numbness, tingling or “pins and needles,” at the affected nerves' dermatomes. This paresthesia, if properly directed and produced at the necessary levels, can “mask” certain forms of chronic pain.
The focus, characteristics and intensity of the generated electric field are determined by the electrode configuration (i.e., the polarity, if any, assumed by each electrode) and the electric pulse waveform (collectively “stimulation setting”). The waveform properties include, at least, a stimulation frequency, a stimulation pulse width and phase information.
SCS systems are of two types. The most common system is a totally implanted pulse generator (IPG). An IPG consists of a surgically implanted, internally-powered, pulse generator and, typically, a single multi-electrode lead. Once implanted, the IPG may be activated and controlled (programmed) by an outside telemetry source. The patient, being largely relieved of daily interaction with the system, uses a small magnet to both turn the system on and off, and limitedly control the stimulation settings. The internalized power source limits the life of these systems to between two and four years. After the power source is expended, the patient is required to undergo replacement surgery to continue electrical stimulation.
The second type of SCS system is a radio frequency (RF) system. An RF system consists of a surgically implanted, passive receiver and a transmitter which is worn externally. The transmitter is connected to an antenna which is positioned, externally, over the site of the implanted receiver. In operation, the transmitter communicates, through an RF signal, to the implanted receiver. Just as with the IPG system, electrical stimulation is delivered via implanted leads. Differing from an IPG, however, RF systems typically posses greater power resources, thereby enabling RF systems to utilize multiple leads. An RF system, like the one described herein, is disclosed in U.S. Pat. No. 4,612,934, issued Sep. 23, 1986 to Borkan.
Although existing systems have proven effective, these systems provide only qualified relief to patients who experience multi-focal or complex pain. Current SCS systems can address, at a maximum, two distinct pain patterns—a “pain pattern” being a dermatome, dermatome segment or series of dermatomes afflicted by pain. One current system features two percutaneous leads, wherein the user can elect to address up to two unilateral pain patterns or a single non-complex, non-migrating bilateral pain pattern.
“Unilateral pain” is said to be that pain which is localized on one side of the patient's body or the other. Unilateral pain is most efficiently, addressed through a “unilateral electrode array,” or a lead which is positioned to one side or the other of the physiological midline of the spine, e.g., an electrode positioned to the left of the physiological midline typically addresses pain located on the left side of the patient's body. Therefore, logically, “bilateral pain” is that pain which affects both sides of the patient's body, for example, lower back pain is often considered bilateral in nature. A bilateral electrode array generates an electric field to address bilateral pain. A bilateral electrode array may take two forms: (i) a single multi-electrode array positioned on or immediately about the physiological midline of the patient; or (ii) two parallel multi-electrode leads positioned to either side of the physiological midline, in which the leads produce a single electric field which transverses the spinal cord. As began above, the system of this example can be configured to address two unilateral pain patterns or a single bilateral pain pattern. The limitation inherent with this system is that a patient can experience only “either-or” pain management. Therefore, the patient is restricted to the simplest form of “multi-focal” stimulation applications.
For those patients whose pain does not conform to the non-yielding stricture of prior art systems, it would be desirable to provide an improved SCS system, whether an IPG or RF system, which could accommodate three or more stimulation settings to address diffuse, multi-focal pain, whether of a unilateral or bilateral nature or any combination thereof. A further desire would be to allow a patient, at will, to tailor a stimulation treatment from a group of programmed stimulation settings, wherein the patient may select: (i) a single stimulation setting, (ii) any number of stimulation settings from the programmed group, the selected settings being administered “simultaneously” or (iii) “simultaneous” stimulation of all programmed stimulation settings. “Simultaneous” stimulation being a mode of operation wherein each selected stimulation setting is delivered to the patient, the patient receiving the cumulative effect of each stimulation setting, and not substantially perceiving the transition from one stimulation setting to another.
In addition to the use of this technology for pain management, some researchers believe that SCS may have beneficial application in obtaining relief from and/or controlling the physical effects of peripheral vascular disease (PVD), angina pectoris, and various motor disorders.